CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income	$ 14,678	$ 41,854	$ 74,052
OTHER COMPREHENSIVE (LOSS) INCOME, NET OF TAX:
Unrealized loss on available-for-sale securities, net of tax of $46, $3, and $4, respectively	(83)	(4)	(6)
Employee benefit plan:
Actuarial (loss) gain on retirement plan, net of tax of $218, none and $488	(388)	(385)	413
Plan amendment cost, net of tax of $3,305, none and none, respectively	(5,963)	0	0
Amortization of plan amendment cost, prior service cost and actuarial loss for retirement plan included in net periodic pension costs, net of tax of $553, $209 and $238, respectively	997	375	927
Net change for employee benefit plan	(5,354)	(10)	1,340
TOTAL OTHER COMPREHENSIVE (LOSS) INCOME	(5,437)	(14)	1,334
COMPREHENSIVE INCOME	9,241	41,840	75,386
Unrealized loss on available for sale securities, tax	46	3	4
Actuarial (loss) gain on retirement plan, tax	218	0	488
Plan amendment cost, tax	3,305	0	0
Amortization of prior service cost and actuarial loss for retirement plan included in net periodic pension costs, tax	$ 553	$ 209	$ 238